This invention relates to improved reinforced thermoplastic molding compositions and more particularly to fibrous reinforced polyoxymethylene molding compositions.
As is well known, polyoxymethylene, or polyacetal, is a thermoplastic resin which finds wide utility in the manufacture of molded articles. Molded articles of exceptional strength and toughness are obtained when the polyoxymethylene resin is intimately combined with various reinforcing agents.
In the past, however, it has been found that various additives are required to provide the desired physical properties to the molded article prepared from the reinforced polyoxymethylene polymers. Inferior physical properties commonly can be traced to poor adhesion between the polymer and the fibrous reinforcement.
Thus, for example, U.S. Pat. Nos. 3,542,722, 3,883,468 and 3,963,668 disclose polyoxymethylene resins filled with glass fibers which have been treated with adhesion promoting organosilicone materials.
U.S. Pat. No. 3,647,743 discloses that glass reinforced polyoxymethylene polymers, having particularly improved impact strength, are provided by coating the surface of the glass-fibers with styrene type resins and then mixing with the polyoxymethylene polymer. Other glass reinforced polyacetal compositions, wherein the glass reinforcement has been coated with an epoxide group containing silane adhesion promoter are also referred to in U.S. Pat. No. 3,850,873.
Other U.S. Patents, typical of which is U.S. Pat. No. 3,455,867, disclose the use of chemical coupling agents to provide the required adhesion between the glass fibers and the polyacetal; and
U.S. Pat. No. 4,111,887 discloses the utilization of a polycarbodiimide and optionally a phenoxy resin to provide an improved reinforced polyoxymethylene molding composition.
While certain satisfactory results have been achieved by these heretofore known compositions, there is still a need for further satisfactory fiber reinforced polyoxymethylene compositions with even more improved physical properties.